1. Field of the Invention
The present invention relates to a fan device with improved speed control module and, more particularly, to a fan device for constructing a plural fan system with automatic speed adjustment.
2. Description of the Related Art
A conventional speed control module shown in FIG. 1 includes a control unit 91 and a signal output circuit 92. The control unit 91 has a signal input port 911 for a pulse width modulation signal (PWM signal) to be inputted into the control unit 91, a signal output port 912 connecting with and transmitting a state signal to the signal output circuit 92, and a command output port 913 connecting with and transmitting a command signal to a driving unit 93 of a fan controlled by the conventional speed control module. Furthermore, the signal output circuit 92 has a transistor 921 that acts as an electrical switch for the signal output circuit 92 to output a digital signal according to the state signal. Thereby, the control unit 91 receives the PWM signal through the signal input port 911 and generates the command signal corresponding to the PWM signal to operate the fan. Besides, according to a state of the fan, which is identified as a normal state or an abnormal state, the state signal transmitted to the signal output circuit 92 is at a HIGH voltage level or a LOW voltage level, and the signal output circuit 92 amplifies the amplitude of the state signal to form the digital signal for being in further use. However, while a plurality of the above-mentioned fans constructs a plural fan system, with each fan being controlled by the above-mentioned speed control module, an operation of the plural fan system with well coordination of the fans is unachievable if only a parallel connection between the fans is applied. Namely, the fans constructing the plural fan system separately work without adjustments in speed when any one of them is in an abnormal or broken state that reduces blowing efficiency of the plural fan system.
Alternatively, when a plural fan system able to automatically change speeds of normal fans thereof during a breakdown period of any fan of the plural fan system is required, a control center circuit connecting to the signal output circuits 92 of all the fans and able to respectively adjust the PWM signals entering the control units 91 is necessary. Thus, the control center circuit adjusts the PWM signals according to the digital signals formed by the signal output circuit 92, so as to change the speeds of the normal fans and maintain blowing efficiency of the plural fan system. However, the control center circuit not only increases manufacture cost of the plural fan system, but also has to be replaced with another one when a demanded number of fans constructing the plural fan system is changed.
Another conventional speed control module applied in a plural motor fan system is described in U.S. Pat. No. 4,988,930 entitled “PLURAL MOTOR FAN SYSTEM WITH IMPROVED SPEED CONTROL”. The conventional speed control module is for speed control over a first DC fan and a second DC fan, with the two DC fans connecting with each other in parallel and at least one of them providing two speed levels. Besides, the conventional speed control module is a circuit with a plurality of electrical switches, and the two DC fans are fed with a DC power passing through the said circuit. Thus, by controlling each of the electrical switches open or close, the speed control module can select the speed levels of the two DC fans, so as to change the speeds of the DC fans.
Nevertheless, states of the DC fans are not automatically sent to the conventional speed control module, and thus automatic control over the electrical switches of the speed control module for speed adjustment of the DC fans corresponding to states thereof is unachievable. In other words, the conventional speed control module is unable to raise the speed of one of the DC fans immediately and automatically for maintaining blowing efficiency of the plural motor fan system during a breakdown period of the other DC fan. Moreover, the conventional speed control module still has to be replaced with another one when a demanded number of fans used in the plural motor fan system is changed. Hence, there is a need for an improvement over the conventional speed control module.